A class of echinoderms (Echinodermata) restricted to the Lower and Middle Ordovician, which had biserial brachioles, well-developed pentameral symmetry, and ambulacra composed of biserial plates.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。